Periodontal disease (PD) pathogenesis is characterized by a chronically elevated immune response to the oral flora. Multiple immune cell types play roles in PD, with lymphocytes infiltrating the site of infection relatively late in disease progression. In patients with the most severe PD, the majority of cells in the gingival lesions are B cells. These findings suggest that B cells play a dominant role relatively late in PD pathogenesis. However, the function of B cells in PD has not been rigorously established in vivo. Our recent demonstration that B cells from PD patients constitutively secrete cytokines was accompanied by the discovery of an elevated percentage of Toll-like receptor (TLR) 2 and TLR4-positive B cells in human periodontal lesions and PD patient blood. Functional analyses demonstrate that B cell TLR2 and TLR4 activation generally results in production of pro- inflammatory and osteoclastogenic cytokines. Additionally, TLR4 ligand decreases TLR2-mediated production of IL-10, an important anti-inflammatory cytokine. The discoveries of an elevated percentage of TLR-positive B cells in PD patients, the overall pro-inflammatory responses of these B cells to TLR ligands, and the prevalence of B cells in PD lesions indicate that B cell TLRs play important roles in PD by regulating inflammation thus bone loss. Because the oral flora provides innumerable TLR ligands, our preliminary data predict that B cell TLRs promote inflammation directly through cytokine activation in vivo. Although additional studies on human B cell TLR function are likely to be mechanistically and clinically important, the next critical step in this line of investigation is to unequivocally demonstrate B cells and B cell TLRs play a role in PD. We hypothesize that B cell TLRs promote inflammation and bone loss thus exacerbate PD. We will test this hypothesis in the oral gavage mouse model of PD to determine how 1. absence of B cells; and 2. TLR2 or TLR4 expression only on B cells affect PD pathogenesis. These studies will unequivocally demonstrate roles of B cells in PD to significantly expand the understanding of basic B cell biology in mucosal inflammatory diseases. PUBLIC HEALTH RELEVANCE: Periodontal Disease (PD) is a common infection linked to serious complications including cardiovascular disease. Novel PD treatments are needed to supplement current regimens, which have limited effectiveness in many patients. Although the immune system plays an important role in PD, the importance of one immune cell type, B cells, is poorly understood. New evidence from PD patients suggests that B cells play important roles in PD, but human subjects research, by its nature, cannot definitively link B cells to disease pathogenesis. The project proposes to test the role of B cells and their surface receptors in PD using model organisms with a long-term goal of identifying new treatments for PD.